This is a pretty long story, and I probably sound stupid, but I'm genuinely concerned, so...

I've had an R4 with YSMenu (using a2h's Auto-Generator, if it matters) for a while; it's been working beautifully. I got the supposed "latest" extinfo/infolib/savlib.dat (this one from Scorpei's compatibility list) in order to play WarioWare DIY. It was all going fine until I decided to put Sonic Rush on the microSD this morning. I played it for a while, then shut it off - the next time I turned my DS on, attempting to select Sonic Rush from the menu made the DS promptly freeze; the icon for the game wouldn't even show up - it would still show the icon and information of the game I had selected right before it, and it would be stuck on the menu, rendering me helpless to do anything but turn it off. Trying this on a few other games, I'd found out that creating a save file makes the R4 freeze completely.
Afterwards, I found out that downloading games via Wi-Fi in DIY makes it freeze as well, something that worked fine up until now.